Despite therapeutic advances, treatment of adult ALL results in long term survival of only 30-40% of patients, with a significantly worse prognosis for patients over the age of 60. There are 2 sub-projects, one of which will be entering clinical trial in the near future. 1. The PARP Inhibitor ABT-888 Potentiates the Anti-Leukemic Activity of Temozolomide in Human Acute Leukemia Cells with Limited DSB Repair Capacity. Purpose: Adults with poor prognosis acute leukemias have few therapeutic options due to genetic lesions rendering leukemic blasts resistant to therapy, and the toxic nature of aggressive therapies in heavily pretreated and/or elderly patients. The goal of this study was to determine the potential in vitro efficacy of a regimen combining inhibition of base excision repair (BER) using the poly(ADP-ribose) polymerase (PARP) inhibitor ABT-888 with temozolomide (TMZ) against human leukemia cell lines and primary cells as a prelude to a potential phase I/II clinical trial of this regimen. Experimental Design: Leukemia cells were cultured in the presence of ABT-888 or TMZ alone or in combination at concentrations and times that approximate what is clinically achievable, and inhibition of cell proliferation, induction of apoptosis, and cell cycle checkpoint activation were monitored. The kinetics of induction of DNA double strand breaks (DSB) and their repair was monitored by immunohistochemical determination of &#61543;-H2AX and Rad51 focus formation. Results: Culture in TMZ or ABT-888 as single agents have limited anti-leukemic activity, however the combination demonstrated enhanced anti-leukemic activity on approximately half of the cell lines and primary isolates tested. Efficacy of the combination was not dependent on the level of endogenous PARP activity, nor on the lineage (lymphoid versus myeloid) of the leukemic blasts. Both sensitive and resistant cells demonstrated a similar S/G2 arrest with rapid activation of Chk1 and Chk2, however, in the continued presence of inhibition of BER, only resistant cells could repair DNA DSB, indicating that other repair pathways, probably homologous recombination (HR), play a critical role in determining the cells fate after treatment with this regimen. Conclusion: The combination of TMZ and ABT-888, when used in vitro in a pulse manner similar to the clinical application of these drugs, leads to enhance killing of leukemia cells, and that efficacy it determined by the capacity of the leukemic blasts to repair DSB. Based on this laboratory work, a clinical trial has been approved by CTEP and will be distributed to co-investigators this week. In this trial adults with relapsed or refractory AML or ALL;Ph+ ALL if failed 2 tyrosine kinase inhibitors;CML in accelerated phase or blast crisis having failed two tyrosine kinase inhibiors;AML arising in the setting of antecedent MDS, MPD, or secondary leukemia;de novo AML or AML in patients older than 60 with poor prognostic features or who are unwilling to receive standard induction therapy. Patients will be treated with temozolomide (TMZ) 150 mg/m2 for 7d with 10 mg PO BID of ABT-888. If this is tolerated, TMZ will be increased to 200 mg/m2 d1-7 with 10 mg BID ABT-888. If tolerated the dose of ABT-888 will be escalated up to 80 mg/m2 or MTD, whichever comes first by standard phase I dose escalation criteria. Translational studies will include measurement of MGMT protein levels, PAR levels pre and post treatment using an NCI-validated immunoassay, analysis of gamma-H2AX foci as measure of DS DNA breaks, and determination of mismatch repair status in patients with low MGMT levels. Endpoints are: Primary Objectives 1.To define the maximum tolerated dose (MTD) and Recommended Phase II Dose (RP2D) of ABT-888 administered in combination with temozolomide in patients with acute leukemias. 2.To evaluate the feasibility, safety, and toxicity of administering ABT-888 in combination with temozolomide in patients with acute leukemias. Secondary Objectives 1. To document responses in acute leukemias. 2.To observe the pharmacokinetics of both ABT-888 and temozolomide when administered alone and in combination. 3.To study the pharmacodynamics: a) to determine the levels of poly(ADP-ribose) (PAR) before and after administration of ABT-888 and temozolomide in patient leukemia blasts;b) to analyze methyl-guanine methyl-transferase (MGMT) protein levels in primary leukemia blasts;c) to quantify the induction of &#947;-H2AX and RAD51 foci in patient leukemia blasts after treatment;d) to determine whether PARP inhibitor ABT-888 affects non-homologous end-joining (NHEJ) repair activity in vivo and whether ABT-888 reduces the frequency of NHEJ repair errors. 2. The second project involved study with a pan-Akt inhibitor from Abbott labs called A443654. We have accumulated extensive data with cell lines and primary cells demonstrating the activity of this agent alone and in combination with proteasome inhibitors and inhibitors of Bcl-2/Bcl-XL. The latter studies are especially interesting and demonstrate synergistic induction of apoptosis withing a few hours of treatment, suggesting that drug availability in vivo may not be limiting. We are visiting CTEP next week, and will discuss what studies are needed to move these concepts into the clinic.